1. The Field of the Invention
The present invention is related to chemical detection. More specifically, the present invention relates to devices for detecting volatile chemical reagents.
2. The Background Art
Fluorescence quenching analysis may be used to detect volatile chemical reagents. The volatile chemical reagents detected through fluorescence quenching analysis are known as electron acceptor molecules. Throughout this application, the terms volatile chemical reagent and electron acceptor molecule will be used interchangeably. Fluorescence quenching is the decrease in the fluorescent emissions intensity that occurs when an electron acceptor molecule associates with the fluorescent sites on a fluorescent material. The Stern-Volmer constant, or quenching constant, is a representation of an electron acceptor molecule""s ability to quench the fluorescence of another material. The Stern-Volmer constant is often referred to as the quenching constant of a particular acceptor molecule with a fluorescent material because the constant depends on both the acceptor molecule and the fluorescent material. The quenching constant for a particular acceptor molecule can be changed by changing the fluorescent material. A fluorescent material is suitable for detecting a particular acceptor molecule only if the quenching constant of the acceptor with the material is sufficiently high to cause a detectable decrease in the fluorescent emissions intensity.
The discovery of a large quenching constant (1.7xc3x97107 Mxe2x88x921) between the fluorescent material poly (2,5-methoxy-propyloxysulfonate phenylene vinylene)(MPS-PPV) and the acceptor molecule methyl viologen (MV2+) provided the basis for a new class of highly sensitive chemical detectors. This class of detectors utilized many combinations of well-known, ionic acceptors and fluorescent materials. The fluorescent materials in this class of detectors consist essentially of neat conjugated polymers.
These detectors typically comprise a neat fluorescent conjugated polymer, a means for exciting the polymer, and a means for monitoring the fluorescent emissions intensity over time as the polymer is exposed to gaseous samples. Through research and calibration prior to inclusion in a detection device, these neat conjugated polymers may be used for determining the presence and concentration of one or more volatile chemical reagents in a gaseous sample.
Neat fluorescent conjugated polymers are known to be useful in detecting methyl viologen and other ionic electron acceptors with quenching constants as high as 107-109 Mxe2x88x921. However, when a neutral acceptor molecule is used to quench the neat fluorescent polymer, the quenching constant can be as much as five orders of magnitude lower. For example, when MPS-PPV is quenched by a neutral acceptor molecule such as 2,4,6-trinitrotoluene (TNT) the quenching constant is 1.02xc3x97104 Mxe2x88x921. Such a low quenching constant associated with neat fluorescent conjugated polymers renders them unsuitable for detecting neutral acceptor molecules.
A conjugated polymer""s fluorescent emissions are quenched when acceptor molecules associate with the fluorescent sites on the polymer. Unfortunately, the association of the acceptor molecule with the neat polymer is mostly irreversible, even under vacuum. In some applications only 10% of the initial fluorescence can be recovered after the exposed conjugated polymer is under vacuum (10xe2x88x923 torr) for ten minutes. The difficulty in removing the acceptor molecules from the polymer may be due to changes in the morphology of the polymer or due to the strong dipole-dipole interactions between the electron rich polymer and the electron deficient acceptor molecules. Non-reversible quenching makes chemical detection through fluorescence quenching of neat conjugated polymers costly and inefficient.
A disadvantage of chemical detectors that rely on fluorescence quenching methods using neat conjugated polymers is that they are only useful for detecting charged electron acceptors. Thus, hazardous neutral chemicals such as TNT, which is a signature agent for land mine detection, are not detectable. A further disadvantage of such chemical detectors is that they are expensive and difficult to maintain. A new sample of the neat fluorescent polymer must be prepared for each subsequent use of the detection device because the fluorescent polymer used in the detection is not reusable. Furthermore, ensuring the consistency of the device is difficult because each fluorescent polymer sample must be identical to ensure identical quenching behavior.
Therefore, it would be advantageous to provide a chemical detection device capable of detecting both neutral and ionic electron acceptor molecules. It would be a further advancement to provide a fluorescence quenching detection device that is reusable. Such a device is disclosed and claimed herein.
The present invention is directed to a device for detecting volatile chemical reagents in gaseous samples. The device utilizes a fluorescent material comprising a polymer-surfactant complex to detect specific chemical reagents within the gaseous sample. The polymer-surfactant complex is formed between a fluorescent, ionic conjugated polymer and an oppositely charged surfactant. In addition to the fluorescent material, the device further comprises a contact region where the gaseous sample may associate with the fluorescent material, a light source that emits fluorescence-inducing light directed towards the fluorescent material, and a detector that detects the fluorescent emissions intensity from the fluorescent material. The use of a fluorescent material comprising polymer-surfactant complexes enhances the material""s fluorescent emissions intensity, enhances the material""s quenching constant in the presence of neutral electron acceptor molecules, and allows the device to be reusable.
The fluorescent polymer-surfactant complex that is used in the fluorescent material may be formed in a polar solution. The polymer and surfactant may be added to a polar solvent to create a ratio of surfactant molecules per monomer repeat unit of polymer ranging from about 1:1 to about 1:10. One presently preferred ratio is about 1:3 when the fluorescent material includes polymer-surfactant complex solution.
Fluorescent material of the present invention may also include a polymer-surfactant complex film. The film may be a bilayer film with an outer layer of oppositely charged surfactant covering a film of fluorescent, ionic conjugated polymer.
The film used in the fluorescent material may also be formed from a solid precipitate that is formed by complexing a fluorescent, ionic conjugated polymer with a sufficient quantity of oppositely charged surfactant to cause precipitation. The precipitate may be formed by complexing the polymer and surfactant in a ratio of surfactant molecules per monomer repeat unit of polymer of about 1:1. The film formed from the precipitate may be formed by spin coating the precipitate from a solvent, by casting, or by other methods known in the art.
The light source directed at the fluorescent material emits at least a portion of its light at the excitation wavelength of the polymer-surfactant complex causing it to fluoresce.
The detector may comprise a detection device and an output device. The detection device receives fluorescent emissions from the polymer-surfactant complex, converts the emission intensity into electronic signals, and communicates the electronic signals to the output device. The output device transmits the intensity of the fluorescent emissions received by the detection device for analysis.
The present invention is also directed towards a reusable device for detecting volatile chemical reagents in a gaseous sample. A vacuum evacuates the gaseous sample from the region of the fluorescent material after the material has been exposed to the gaseous sample.